Signs for the display of three discrete messages in a serial fashion are known. In such signs, an array of triangularly sectioned sign elements having message display faces every 120.degree. are utilized. A drive shaft extending across the array effects the desired simultaneous rotation of the array. Preferably, the sign elements display a first message for a given increment of time. Thereafter, substantial simultaneous rotation of the sign elements in an 120.degree. increment occurs--usually by effecting rotation of the individual triangular sign elements in a cascading sequence starting at one end of the sign element array and cascading in rotation to the other end of the sign element array. As a result, three sign messages can be displayed in sequence.
Special cams have been devised to effect the rotation of such signs. A particularly advantageous cam arrangement is disclosed in Swedish Patent No. 7706713-0 issued Sep. 13, 1982 to J. E. A. Hakala. In this device it is disclosed to have rotating "butterfly" cams permanently fixed to a common shaft. These rotating butterfly cams each mesh with and rotate triangular followers on each of the discrete sign elements.
The butterfly cams are so configured that for 270.degree. of rotation, the triangular sectioned sign elements are held in place and not driven. It is during this interval of time that one of the three serial messages of the sign is displayed from the temporarily stationary triangularly sign elements. During the remaining 90.degree. of butterfly cam rotation, driving of the triangular sectioned sign elements occurs. This driving causes rotation of the triangular section of sign elements by increments of 120.degree..
Since the triangular sectioned sign elements have three message display surfaces, one of the three message displaying surfaces is rotated out of view while the serially next in order message displaying surface is rotated into view. By repeating this mechanical sequence at butterfly cams driving the triangularly sectioned sign elements of an entire array, the entirety of a sign element array displays in serial sequence its three discrete messages.
Such prior art signs have had in their application three discrete problem areas. These problem areas include the removable attachment of the message displaying faces to and from the array of rotating triangularly sectioned sign elements, and the positioning of the driving elements of the sign to the discrete triangular sign elements for the substantially simultaneous rotation and display of the sequential messages.
Posting of the message displaying faces to the rotating triangular sign elements has further not been without problems in the prior art. Specifically, the fastening of a single message displaying surface to one side of the triangular sign element has required the cooperation of at least three parts. One part is the message displaying surface itself, which surface has heretofore been constructed of a substantially non elastic material, usually metallic. A second part is the individual rotating triangular element of the sign; this rotating triangular element is also not flexible. A final part has been an elastic interface fitting between the rotating triangular sign element and message display, ridged or elastic. This interface fitting is typically conformable. It functions to conform interlocking grooves between the message display elements and rotating triangular sign element. See, for example, U.S. Pat. No. 4,528,763 issued Jul. 16, 1985 to Ahearen for Sign Having Changeable Displays.
Attachment of such message display elements is difficult. Since both the message displaying surfaces and the rotating triangularly sectioned sign elements are substantially non elastic, they must be fitted with a top to bottom snapping effecting simultaneous trapping and conforming of the elastic interface fitting.
The mounting of the butterfly cams with respect to the following triangular sign elements has constituted another major problem area. Thermal differential expansion has plagued prior art sign designs. For outdoor advertising purposes, such signs are in the order of 48 feet in length and have 144, 37/8 inch wide individual rotating triangular sign elements. Mounting the driving butterfly cams to a common shaft and having the driving butterfly cams mesh with triangular followers at precise on center spacings has not been achieved. In the prior art, the butterfly cams--typically of made of plastic--have been fixed to a rotating metallic shaft--usually made of steel. The framing of the sign elements--defining the side-by-side spacing of the triangular sign elements of the array is fabricated from a different material--usually metallic.
As the sign encounters thermal expansions common to an outdoor advertising sign environment, the drive shaft, sign housing and sign element spacings change with differential thermal expansions. Cam spacing moves out of the original assembled alignment of the sign. Binding of the butterfly cams and triangular followers effecting the desired serial rotation of the triangular sign elements can and does result. Unnecessary energy occurs in sign element rotation. Mechanical failure of the sign element array drive follows.
Because of at least the foregoing difficulties, such triangular sign element arrays have not been widely used--despite the more efficient and interesting display of their serial messages.